This invention relates to apparatus for stormwater retention and release, and a method of use thereof. The invention relates more specifically to, but is not limited to, apparatus for stormwater retention and release from a property development.
The term stormwater encompasses water deposited by the weather, and includes snow, hail, rain and ice.
Property developments, especially residential developments, more frequently require that stormwater draining from the property is retained prior to its controlled release in order to reduce flood risks downstream of the site, or to control flows of existing points of outfall with limited spare capacity. Frequently, rates of stormwater discharge from property developments are carefully controlled and restricted, certain controlled rates being set to particularly low levels resulting in large balancing means being necessary to retain the stormwater prior to its controlled release.
The two most frequently used solutions to retain stormwater comprise providing balancing means in the form of a pond or a relatively large tank located in an open space area proximal to the development. If a tank is provided, it may be located under a highway as part of a box culvert. Stormwater collects in the tank or pond and is retained therein prior to release through suitably dimensioned outlets into a local drainage network, usually a sewer.
Ponds are less favoured by developers as they require regular maintenance, and controls connecting the pond to a local drainage network are susceptible to blockage by debris fang into or otherwise gaining access to the pond. Tanks, however, are expensive and also require regular maintenance. Often, developable land must be sacrificed in order to accommodate the pond or tank.
Furthermore, ponds and tanks of the prior art type are laborious to install. Large sewers, usually in the form of relatively large diameter pipework, or box culverts, must be installed underground which requires a significant amount of effort.
Whilst not concerned with control of stormwater control at property developments to reduce flood risks there is disclosure in EP 08253304 A2 of apparatus for separating floating and non-floating particulate from drain water in sudden storms and in steady prolonged rainfall. A tank is connected to inlet and outlet conduits to provide a level of drain water between the conduits and includes particulate containment chambers in which particulate is collected from the water passing through the bank from the inlet to the outlet conduit. In one embodiment a detention basin is provided in combination with the tank into which excessive drain water resulting from higher than usual water flow rates is diverted from the tank. Drain water from the detention basin returns to the tank by a one-way valve for exit from the outlet conduit once the sudden influx of water has passed. The diverted water enters the detention basin at a much higher level than the entry to the outlet conduit, which is in the lower region of the tank. The one-way valve is at the level of the entry to the outlet conduit so that the water is encouraged to leave the detention basin as soon as the sudden influx of water passes. This disclosure is essentially concerned with removal of particulate in a sewer system rather than drain water storage to reduce flood risks.
DE 29611700 U1 discloses the collection of rainwater underneath a building but this is to provide a reservoir of the water for pumping to shower/washing facilities in the building and is not intended to reduce flood risk at a property. Drainage pipes simply feed and drain water directly into and from the foundations of the building where the water is collected.
There is a need in the art for apparatus which can effect stormwater retention and where necessary, controlled release of stormwater from a property development, which overcomes problems discussed above.
According to a first aspect of the invention there is provided stormwater retention apparatus adapted in use to retain stormwater prior to release of the stormwater from a property comprising:
a closed container which in use is located underneath or proximal to a building of the property, being operatively connected in use by at least one inlet conduit to drainage means sourced externally from the building to receive stormwater into the container, and being further operatively connected in use to at least one outlet conduit by which stormwater is led away from the container and
a control chamber with which the container is in fluid communication and through which stormwater enters, to be stored in, and leaves the container when the stormwater reaches a determining level (W) in the control chamber spaced above the base of the container,
characterised in that the inlet and outlet conduits are connected to the control chamber and thereby to the container, and that the outlet conduit comprises an end portion which passes out of the control chamber and includes an entry spaced above the determining level (W) by which stormwater can pass from the control chamber into the end portion to exit from the control chamber, and which by being spaced above the determining level (W) allows stormwater to collect in the container and control chamber above the determining level (W).
The property may be one of a series of properties on a property development. Preferably each property in such a development has stormwater retention apparatus according to the first aspect of the invention, the stormwater exiting from the container of each apparatus into a local sewer.
Preferably the container is subterranean, located under part of the property. Where the property is a house having a garage, the container is conveniently located under the garage, for example.
Advantageously, no pond or tank is required, freeing all available developable land. As the container of the or each stormwater retention apparatus and its conduits are of a considerably smaller scale than prior art ponds and tanks, considerably less effort is required to install apparatus according to the first aspect of the invention.
Furthermore, the apparatus is less susceptible to blockage as very little debris can gain access to the container as it may be sealed off from the environment. Small amounts of debris, such as leaves, may enter the container via the drainage means fitted to the property, but in general are not sufficient to block the entry to the outlet conduit.
Preferably the container is incorporated in the foundations of the property during construction of the property. Preferably the container is made at least in part of bricks and mortar, and may be lined with cement. A waterproof lining may be added to the inside surfaces of the container to prevent leaks occurring.
Drainage means fitted externally to the property preferably comprises guttering and drainpipes which collect stormwater falling on the property, channelling the stormwater to the base of the property and into the container. The drainage means may, however, be any suitable drainage means which is operatively connectable to the container.
The inlet and outlet conduits may be pipes of relatively narrow diameter, for example 75 mm or 100 mm.
Where the discharge from the property is rate limited, the apparatus may include suitable exit rate limiting means. The exit rate limiting means may include a Hydrobrake (Registered Trade Mark). The outlet conduit may include an orifice which is suitably dimensioned so as to restrict the flow of stormwater through the orifice to a predetermined level.
Where no discharge rate applies, no exit rate limiting means is required. In either case, the need for a large tank or pond is obviated by the provision of apparatus according to the first aspect of the invention.
Stormwater entering the container must first pass through the control chamber. The control chamber may be located above or below ground level, or may be partially below ground level. The chamber may be below ground level at a level relating to the invert of the container. The control chamber may be attached to the side of the property underneath which the container is located.
The control chamber may be operatively connected to the container by a hole or holes located in a wall separating the container and the control chamber. The control chamber may be raised above the level of the container to create a split-level stormwater retention apparatus, the stormwater entering the control chamber and passing under gravity into the container via a hole or holes in the separating wall proximal to the base of the control chamber.
The outlet conduit may comprise at least one outlet pipe, an end portion of which sealingly passes through a hole in a wall of the control chamber. The end portion preferably includes a bend, preferably at 90xc2x0, so that one open end of the outlet pipe is directed upwards, away from the base of the control chamber. In the wall of the pipe on the underside of the bend, opposite to the base of the control chamber, a suitably dimensioned orifice may be provided at a selected level through which a restricted flow of stormwater can pass out of the control chamber when the stormwater in the control chamber reaches that level.
As the stormwater level rises in the control chamber, the orifice does not become obstructed as debris floating in the stormwater also rises. When the stormwater level rises above the height of the orifice, a small jet is created from the orifice into the pipe, operating under a head of stormwater and ensuring that the orifice remains free of debris.
The control chamber may, at its base, be fitted with a silt trap in which biodegradable debris such as leaves can collect without blocking the passage of stormwater into or out of the container. A weir or weirs to the inlet conduit or conduits may also prevent any solid passing to the container or obstructing the orifice.
In the above-described form of the outlet conduit, the upwardly-directed open end of the outlet pipe acts as an overflow outlet. If the stormwater level in- the container rises above the level of the open end of the outlet pipe, stormwater enters the pipe via the open end of the pipe (in addition to exiting via the orifice situated on the underside of the bend portion of the outlet pipe). The open end is preferably capped with a device which prevents debris entering the outlet pipe in the event of an overflow. The device may be a bird-cage cap to prevent debris accessing the outlet pipe and rodent access into the container from a downstream sewer network.
In order to prevent condensation and damp causing damage to the foundations and underside of the property above the container, air bricks may be included in the upper regions of the foundations to allow venting of water vapour. The air bricks may be provided with insect screens to prevent debris entering the container. The air bricks may also provide a second means of overflow.
Polythene membranes or other waterproof coating such as xe2x80x9cSYNTHAPRUFExe2x80x9d (Registered Trade Mark) could be used to line the walls or underside of the floor of the property to protect the property from structural damage caused by damp. In this way, the property is protected from the deteriorating effects of damp as condensation is isolated by the membranes. In any event, it is designed so that stormwater would normally only be retained in the container for a relatively short period after entering the container.
A pump may be provided which pumps stormwater out of the container to recycle the stormwater for other uses, such as watering a garden, flushing toilets or washing a car.
According to a second aspect of the invention there is provided a property comprising a building characterised in that it includes stormwater retention apparatus according to the first aspect of the invention
According to a third aspect of the invention, there is provided a method of retaining and controlling discharge of stormwater collected by drainage means fitted to a building, the method comprising the steps of collection of stormwater by said drainage means, retention of the stormwater by stormwater retention apparatus according to the first aspect of the invention, and controlled release of the retained stormwater by the stormwater retention apparatus into local drainage facilities.